Subscription television system



Oct. 6, 1959 P. H. wElss SUBSCRIPTION TELEVISION SYSTEM k SUBSCRIPTIONTELEVISIN SYSTEM Filed Feb. 21, 1958 5 sheets-sheet 2 anaal/ys Gct. 6,1959 Fi1ed"Feb 21, 1958 P. H. WEISS SUBSCRIPTION TELEVISION SYSTEM 5Sheets-Sheet 3 LA... vvvvv Oct, 6, 1959v P. H. wl-:lss

SUBSCRIPTION TELEVISION SYSTEM 5 Sheets-Sheet 4 Filed Feb. 21. 1958 W. T51 NQ.. ANN N ,DH/L H. WE/SS INVENTOR.

BY .0770@/VEV5 States 97,3% Patented st. 6, 1959 2,907,316 snnscnirrIoNTELEVISION SYSTEM Phil H. Weiss, Panorama City, assigner, lay mesneassignments, to Paramount Pictures Corporation, New York, N.Y., acorporation of New York This invention relates to subscriptiontelevision ysystems and, more particularly, Vto improvements therein.

In devising arrangements for subscription television, consideration mustbe given to the fact that not everyone who owns a television set willbecome a subscriber. Therefore, in order to insure that asubscriptiontelevision program is intelligibly presented to the .subscribers to thesystem, and not to the general public, considerable efforts will havebeen expended toward transmitting subscription television programs in aform to be unintelligible to` all receivers except for those which haveattachments enabling the receivers to intelligibly present the signalsreceived. The problem of rendering the program unintelligible at thetransmitter and intelligible again at the receiver is not an unusuallydifficult one. YIt must be appreciated that the attachment requiredV ata receiver must be made as inexpensive as possible, since it iscontemplated that a large number Vof subscribers will be Vobtained, and,unless the receiver attachment is minimal in cost, the financial.aspects of the. situation will keep the system small. In view ofallithe operations which a subscription television receiver attachmentmust carry out, this poses a Vdiicult problem.

One otherl aspect of the investigations conducted heretofore has shownthatthe amount of security obtainable for a system was in directrelationship to the vcost of the receiver attachment. In other words,the more encoding applied to a program at the transmitter, the morecostly the decoding attachment required at the receiver. As the codingarrangement at a transmitter was simplied, the cost of the attachment atthe receiverwas decreased', but a point is reached at which such codingcan be readily broken, and thus Vis substantially useless.

An object` of the present invention is the provision of a novelsubscription television arrangement. Y

Another object of the present invention is the provisionv for renderinga subscription television transmission secure against nonsubscribersWhileA maintaining they required attachment at a subscriber receiverinexpensive.

Still another object of the present invention is the provision of anovel arrangement for rendering a subscription television transmissionsecure.

These and other objects of the invention are achieved in a preferredembodiment subscription television system wherein, at the transmitter,the horizontal synchronizing pulse and horizontal blankng pulseV arereduced or replaced bya grey level pulse. A suitable signal for scriberreceiver, an `attachment is'iprovided which vhas means, energized whenthe subscriber wishes to purchase a program, which uses the sine wavesignal for reconstructing a horizontal synchronizing pulse. This isinserted in the composite video signal having the greylevel pulse, atthe proper time. The composite signal thereafter is applied to theantenna terminals of the television receiver. The receiver thereaftershows a picture which is completely acceptable, in accordance withpresent-day standards. Without the attachment, or when a program is notpurchased, an unintelligible picture is presented.

In order to further maintain security of the system, the audio signalswhich usually accompany the program video signals ,are transmitted onthe same channel as the sine wave signal.V On the channel whichtransmits the composite video with grey-level signals replacingsynchronizing signals, there are transmitted audio signalsrepresentative of a barker. These barker ,audio signals lextol thevirtues of the program and also indicate the times it will be presented,as well as the cost. At a receiver, whether subscriber or nonsubscriber,lthe barker signals are reproduced bythe audio system of the televisionreceiver. The subscriber receiver, in addition, has Va switch, which,when a program is purchased, is automatically operated to connect theaudio system of the receiver directly'to an input from the receiverattachment for directlyreceiving the program audio signals.

Ihe..novel 'features that are considered characteristic ofthis'invention are setforth with particularity in the appendedfelaims.The inventionV itself, both as to 'its organization`- and method ofoperation, as well as additionalobjectsfand advantages thereof, WillbestY be un-v Figure 2c is a Wave shape diagram showing a composite lvidea signal reconstituted at a receiverin accordance with thisinvention;

Figure 3 is a circuit 'diagram of the video coding switch arrangementshown in Figure l;

Figure 4 shows a circuit for providing for the circuit shownV in` Figure3 the line-to-line direct-current level using the backporch key signal;

Figure 5 shows a circuit for setting the required bias levels in thecircuit shown in Figure 3;

Figure 6 shows a circuit for generating the switching pulse employed inFigure 3;

Figure 7 is a circuit diagram of a sine wave generator which` may beemployed at the transmitter;

Figure 8is"a block diagram showing how a subscriber television'programmay bedistributed to subscriber receivers; y

Figure 9 is a circuit'diagram of the attachment provided for eachsubscriber receiver;

Figure l0 is one recording arrangement of the purchase ol ya programwhich may be employed; and

Figure 1l is a circuit diagram for converting'a standard received.composite videosignal into `one having grey-level sync,pulses. e.

' Figure lis a block diagram of a suitable structure at a transmitter tomodify it for use in a 'subscription television system in accordancewith this invention. Signals from a source of normaly video signals 10are applied forl a, video coding switch 12. Signals from a source ofhori-V of the usual horizontal blanking and synchronizing signals. By agrey-level pulse is meant a pulse having an amplitude between the blacklevel and the white level of the video signal. The output of the videocoding switch 12 is applied to a transmitter .14. The transmitter alsohas applied thereto audio signals from a barker sound source 16. Thebarker sound source provides signals which inform the listener as to thevirtues of the program to be transmitted, as well as its cost, the timesthat it will be reproduced, etc. The transmitter 14 modulates themodified composite video signals and the barker sound signals on thecarriers in accordance with the well-known method for presentlytransmitting a composite video signal and accompanying program soundsignal. These are then radiated from an antenna 18.

The output of the source of horizontal blanking signals 14 is alsoapplied to a sine Iwave generator 20. The sine wave generator 20generates a 15.75 kilocycle sine wave, whose frequency and phase aredetermined by the horizontal blanking signals. The sine Wave signal isgenerated for the purpose of reconstituting the horizontal sync signalsat a receiver. Actually, other wave shapes having the same phase andfrequency as the sine wave may be employed in its place for thispurpose, as those skilled in the art will readily recognize. Therefore,it is not intended that this invention be limited by the descriptionherein of a sine wave for reconstituting purposes. However, as apractical proposition, a sine wave is most easily generated, uses theleast bandwidth, and may be readily and easily transmitted by air orwire. Therefore, it is preferred. These sine wave signals are applied toa mixer 22, to which is also applied signals from Vthe program soundsource 24 and direct current from an operating potential source 26. Theoutput of the mixer, whichis a combination of the three signals, isapplied to a wire link 28, which is connected to an attachment at eachone of the subscriber television receivers. Since the frequency of thesignals being carried by the wire link is in the audio frequency range,an ordinary, inexpensive, twisted pair of wires may be used. Thus, forthe purpose of installing a subscription television system in largepopulation centers, there is no need to run extensive coaxial cablebetween the transmitter and the subscribei receiver, as has beenproposed heretofore. A cheap and inexpensive twisted pair of wires isused instead to carry one portion of the subscription televisionsignals, the other portion of which is transmitted by air. A wire link,for all intents :1nd purposes, already exists between a televisiontransmitter and a great number of subscriber receivers in the form ofeither telephone lines or power lines.

Figure 2A shows a wave shape diagram of the cornposite video signal,and, more specifically, that portion in the region of a horizontalblanking pulse 32 and a superimposed horizontal sync pulse 30. The levelof the horizontal blanking pulse 32 is 75 percent of the maximum signallevel, which is the level attained by the horizontal sync pulse 30,considered as 100 percent. The 75 percent level of the blanking pulse isthe black signal, and the video signal 34 may go as high as the blacklevel.

Figure 2B shows a wave shape illustrating thecomposite video in theregion of the horizontal blank pulse as it appears after modification,in accordance with this invention. This wave shape is not shownmodulated on the radio-frequency carrier for the purpose of maintainingclarity in the drawings. The video signal portions remain unaffected,but the blanking pulse and sync pulse portions are replaced by a pulsewhose level is in the grey region of the video signal, `or 50 percentofthe maximum signal level attained and whose -width overlaps theblanking pulse width by a half microsecond on either side. This pulse isdesignated as the grey-level pulse 36..

VFigure 2C is a waveshape of the composite video by the receiverattachment. This wave shape is not shown modulated on theradio-frequency carrier, but as it appears after demodulation, tomaintain clarity in the drawings and explanation. This synchronizingpulse 38 is a five microsecond wide pulse which is superimposed on thegrey-level pulse 36 at the same location as was occupied by thesynchronizing pulse relative to the blanking pulse 32. As will be shownlater, the grey-level pulse is used in the restoration of the horizontalsynchronizing pulse. This is done by increasing each grey-level pulseenergy content, or raising its level during the proper interval to thatrequired for horizontal synchronization responsive to the reconstitutingsignal. Effectively, the ratio of reduction at the transmitter iseffectively restored at the receiver. 'I'he inserted horizontalsynchronizing pulse 38 serves the identical function as thesynchronizing pulse 30, as far as the receiver is concerned. The picturepresented at the reproducing cathode-ray tube will be the identical typepresented on the usual commercial television broadcast, with theexception that the edge portions of the picture which are normally blackwill be grey. However, since the picture is widened, so that only thepicture portion is displayed and the black borders are covered bya mask,no deleterious effects are created by the present invention.

Figure 3 is a circuit diagram of the video coding switch 112, shown inFigure l, illustrating how a grey-level pulse signal is inserted intothe composite video signal in place of the horizontal blanking pulse andhorizontal synchronizing pulse. Normal video is applied to an inputterminal 40, and the level of the-signal established is set by thepotentiometer 42. The potentiometer output is coupled through acondenser 44 and resistor 46 to the grid network 50, which is composedof four rectifiers.

a circuit using backporch key signals. This circuit is Vshown in Figure4 and connection is made thereto through the lead designated as K. Tube48 is connected as a cathode follower to one terminal 50A of a bridgeThe opposite terminal 50B of the rectifier bridge 50 is-connected to aterminal 52A of a second rectifier bridge 52, also composed of fourrectifiers which are poled oppositely to the rectifiers comprisingbridge 50. Output from the two rectifier bridges is taken from terminals56B, 52A. Another terminal 52B of the rectier bridge 52 is connected toa cathode-follower tube 54. The grid of the cathode-follower tube 54 isbiased by a. potential source over a lead, designated as C. A suitablepotential source is shown in Figure 5 of the drawings.

A connection is made from one of the two remaining terminals 50C, 52C ofbridges 5f), 52 through two resistors 56, 58 to the cathode of a tube60. This tube has its quiescent conduction current established bypotential received from the bias source shown in Figure 5 over a leaddesignated by the letter B. This tube may be cut off by the negativesignals applied to its grid over a lead designated by the letter A,which is connected to a blanking signal source shown in Figure 6 herein.The

. remaining terminals 50D, 52D of the bridges 50, 52 are signal in theregion of the horizontal blanking period,.as ,f

connected'throu'ghv resistors 62, 64 to the cathode of a tube 66. vThistube also has its quiescent condition established by the bias applied toits grid from the potential source in Figure 5 over the lead designatedby the letter B. Switching signals are applied to this tube 66 over alead designated vas A, which is connected to lthe blanking pulse signalsource shown in Figure 6.

The operation of the switching circuit shown is as follows. During theactual occurrence of the Vvideo signals, the conduction llevels of thetubes 60 and 66 are suchthat the lower rectifier bridge'52 is cut offand the upper rectifier bridge 50 permits the video signalsreceived-from tube 48 to be passed through to a first arnplifier 68. Theoutput of amplifier 68 is applied to the second amplifier 70, the output'of which is applied to the coded video output terminal 72. For purposesof use Avvtlrtlre camera -signal, there `is usually generatedahorizontal blanking pulse at thetrans'mitter, known as the wideblankin'g pulse. Thiswideblanking pulse'hasone microsecond durationinexcess ofthat ofthe vhorizontal blanking pulse 'actually transmittedin ,the composite video signal; '-As shown inFi-gure 6, the widehorizontal blanking 'pulse is appliedto linput'terminalfiiof aphase-inverter tub-e 76; "The output which is 4applied alongthc ilea'ddesignatedi'bythe letter Ato-the grid of tube 60 is obtained from thecathode of the phase-inverter tube 76. The'output applied alongthe leadA to the grid of tube'66 in Figure 3 is obtained fromth'e plate of tube76.`- As is-well known, the `pulses applied'over leads Af `aridfA' willhave the oppositepolarity `and will exist simultaineously.VThe'wide'horizontal blanking pulse which is applied to the inputterminal `74is a negativepulse, in response to which the pulse over theline Awill be positive -and that over line A will be lnegative going.

'The level-setting'circuit for -the -video signal is derived fromthebackporch-key signal generated at the transmitter. vAs 'shownin"Figure-4,'thebackporch key signalV is applied Vto an input lterminal78, which is connected tothe grid of the phase-'inverter tube Sti.V Inresponse to the backporch signal, two opposite polarity pulses arerapplied through-two coupling condensers to a bridgenetwork, consistingof two resistors `82, 84, connected in series, and inparallel'therewith, two seriesconnected rectiers 86, 8S. To the junctionof the two resistors, there is applied a direct-current bias over alead-designated as C from Figure V5. This sets-a D.C. level lat thejunction of the two rectifiers 86, 8S. This junction isconnected over alead Vdesignated byl the letter K-to'the-'correspondingK lead in FigurevEl at the input to the tube 4S. The occurrence of the `backporch keysignal pulses adjusts this level to whatever'is the proper level foraparticular line by enabling the rectifiers S6, S8 to conduct, inaccordance with the D C. level of the video signal.

`Asfshown in Figure 5, the bias-providing circuit for the switcharrangement shown-'in Figure 3 includesa p1u` rali-ty of resistors 90A,9GB, 90C, and 96D, which are connected in series across the source ofoperating potential. The lead -linesr designated by the letters B, C,and v Bare connected to the junction of these resistors. Apotentiometer-92 is connected across resistors 99B and 90C. The movableAarm of-potentiometer 92 is connected `to the lead line designated as C.Condensers 94, 96 bypass to ground any pulse frequency, which maypenetrate into this biassource. 4The setting of the potentiometer 92establishes the bias level ofthey voltageVv applied over lead C to thegrid of tube 54. This establishes the conduction'of that tube, and alsothe potential-'which is applied to the rectifier bridgeV 52 in' Figure3. This potential is established so that when the rectiiier bridge Vi)is cut off and the rectier bridge 52 is rendered conducting, the outputof. the bridge 52, which is applied to tube 68, -will have the.amplitude desired for a greylevel pulse. `In .other words, the value ofthe potential which` is applied across bridge 52 from the cathode oftube 54 is that required to provide a grey-'level potential atthe outputof the bridge.V j.

From what has been described, the operation -of the arrangementV shownin Figure 3 shouldbecome apparent. 4 'l`he2yalues of vthe potentials'appliedover lead lines B- and B are suchv as to maintain the rectifierbridges 50 and '52 respectively conducting andnonconducting intheabsence `of any input overV4 lead lines A and A. When -suchV inputoccurs, then the rectifier bridges 50 and"`52 are made torespe'ctivelyswitch conditions of conductiomwhereby the potential set by the tube 54is theoutput obtained from thetwo bridges and the signal obtained fromthe tube 48 is blocked.

' Reference is now made to Figure 7, which shows a circuit diagramof aAsuitable sine wave generator which rnav'yibe `e'r'nployed at the`transmitter. :The horizontal' blanking signals are applied to the gridof a tube 100.

There is a iirst tuned circuit in the plate of the tube 100 whichisconnected to a second tuned circuit in the grid of a following tube 102.These tuned circuits include the primary and secondary of a transformer104, which are respectively tuned by the condensers 196 and 108.Sincethe iuput'to` the tube 100 is a pulse, the flywheel is employed toprovide as an input to the grid of tube 102 a sine wave havingthefrequency of the horizontal blanking pulses and synchronizedv to bein phase therewith. The output of tube 102 is derived from its cathodeto which another tuned circuit, consisting of an inductance 110 inparallel with a condenser 112, is connected for'the purpose of furtherassuring that 'a pure sine wave output is derived therefrom.

Figure 8 is a block diagram showing how subscriber television programsin accordance with this invention may be.A distributed to subscriberreceivers. At the television studio 12), there are generated the codedvideo program and the barker, and these are transmitted over the antenna18. Theprogram audio, 15.75 kilocycle sine wave, and direct current aretransmitted over a second channel, consisting of the wire 122, whichconnects to the attachments yfor the subscriber receivers. This vwiremay be supported, for example, by a pole 124. From each one of the poles124, the wire is connected through recording equipment 126 to theattachments 12S for each one of the subscriber receivers. The antennas136 for each one of the subscriber "receivers are also connected to theattachments 128, instead of directly to the television receivers 132, asis customary.

Also connected from each attachment to the receivers 132 is a line whichsupplies the program audio when a subscriber nhasV purchased the programbeing transmitted. As will be shown subsequently, the recordingequipment 126 can make a recording indicative of the fact of suchpurchase foreach subscriber.

Figure 9 is a circuit diagrarnof an attachment which is provided formodifying a television receiver so that it may be employed' in asubscription television system in accordance with this invention. Fromeach pole there are connected the two wires carrying the program audio15.75 kilocycle sine wave signals and the directcurrent operationpotential to two terminals 140A, 140B. One of the terminals 145A isconnected to ground. The

other terminal 140B is connected to one contact of V'a push-buttonswitch 142 and also to the nolmally open contact 144A of a paidrelay`144. The other side of the push-button switch 142 is connecteddirectly to the coil of the relay 144. The coil of the relay 144 isconnected through a paid light 146 to ground. Accordingly, when the`push-button 142 is manually depressed, indicative of the desire to buya program, the operating potential existing over the wire link energizesrelay 144, lights the light 146, `andicontact 144A, which is now closed,shunts the push-button switch 142 'and latches the paid relay 144.

The primary o-f an -audio transformer 148 is connected across lthe wirelink. Program audio signals received over the wire link are applied tothe primary i nected directly to the speaker of the television set. The

remaining contact 144D is connected to the driver circuitfor the speakerin the audio circuit of the subscriber receiver. When the paid-up relay144 is not operated, then the audio amplifier in the receiverisiconnected to lthe loudspeaker over contacts 144C and 144D andsupplies audio signals directly to the loudspeaker of the televisionset. When the relay 144 is operated, then contactv 144C moves fromcontact 144D to 144B, thereby connecting the speaker of the subscriberreceiver '7 to the audio transformer 148, and program' audio can then beheard.

' When the relay 144 is closed, its contacts 144A also enable operatingpotential to be ap-plied to the emitter of a transistor 150. Thetransistor base receivesV direct current through the primary oftransformer 148 and through a variable audio choke 156 and a resistor158. Direct-current potential is also -applied continuously through thetransformer primary to the plates of tubes 152 and 154. Condenser 160and variable choke 156 are used to compensate for any phase shiftoccurring in the course of transmission of the sine wave signals. Thesesine wave signals are applied tothe base of the transistor 150. Thechoke 156 blocks or prevents these sine wave signals from being shortedto ground.

The transistor output, consisting of amplified sine wave signals, isderived from its collector. The collector is connected to apulse-shaping network including a resistor 162 in shunt and a condenser164 in series with the collector transistor 150. These, elfectively,differentiate the output of the transistor. Polarity of the signal beingderived from the sine wave is established by means of the diodes 166,which connects condenser 164 to ground for negative wave shapes, anddiode 168, which permits positive-going wave shapes to be 'applied tothe grid of a tube 152. Accordingly, whenever the sine wave receivedfrom the transmitter has a positivegoing phase, the tube 152 is enabledto conduct for a time determined by the values of the network couplingthe collector of the transistor 150 to the grid of that tube. Tubeoperates as a limiter whereby the amplitude of its output remainssubstantially constant.

The antenna 130 of the subscriber receiver is coupled by means of aradio-frequency transformer 170 to the grid of a tube 154. It will benoted that the secondary of the coupling transformer is in series with aresistor 172. This resistor enables the insertion or addition of asignal derived from the cathode of the tube 152 to that existing acrossthe secondary of transformer 170. The cathode of tube 152 has apotentiometer 174 in series therewith, which is coupled through acondenser 176 to the junction between the resistor 172 and the secondaryof the RF transformer 170.

Referring back to Figure 2C of the drawings, it should be appreciatedthat the pulse derived from the sine wave obtained over the wire link isadjusted by coil 156 to occur at a time when the grey-level pulse,modulated on an RF carrier, is being received from the antenna. Thus,the pulse and radio-frequency signals are applied to the grid circuit oftube 154 as a result of which the tube is permitted to amplify theradio-frequency signals during the occurrence of the pulse. This has theeffect of increasing to a predetermined value the ratio of the radiofrequency during the horizontal synchronization interval to the radiofrequency during the video interval. Upon subsequent demodulation, thesignal appears as shown in Figure 2C. It is seen that the result of themultiplication operation by tube 154 has been to increase the grey-levelpulse energy content, orto raise its level during the proper interval tothat required for horizontal synchronization, responsive to thereconstituting signal. Coupling between the output of tube 154 and theantenna terminals of the television receiver is made through a second RFtransformer 178, the primary of which is in series with the platecircuit of tube 154 and the secondary of which is coupled to the antennaterminals of the receiver. It should be noted that the reinsertion ofthe synchronizing signals occurs while the video signals are stillmodulated on the carrier signal and outside of the television receiver.After such reinsertion, the composite video modulated on a carrier isapplied to the receiver antenna terminals for demodulation and otherprocessing as is done to the normally transmitted composite videosignals.

Before switch 142 is operated, the transistor 150 does not receiveoperating potential, and thus no horizontal synchronizing pulses arepresent in the video received. However, the paid-up relay 144 isinoperative, whereby barker signals, which are received by the antenna132, may be applied to the receiver through the tube 154. Afterpush-button switch 142 is operated, transistor 150 is enabled to amplifythe sine wave signal so that horizontal synchronizing signals may bederived therefrom. The paid-up relay 144 switches the loudspeaker in thereceiver from the audio amplifier within the receiver to the output oftransformer 148. The system may be operated without this added secrecyfeature, namely, furnishing program sound over the wire link and barkerover the air, since there is suflicient security in the video signalsbeing received to prevent unauthorized persons from deriving horizontalsynchronizing signals from the signal receiver over the air.

Thus, only the video coding may be employed and any necessity for makingany audio reconnections inside the receiver are eliminated. Anotherarrangement for omitting any wiring connections in the receiver is toprovide the attachment with an audio amplifier and speaker whereby itmay reproduce the program sound. No switching is required. When theprogram sound is heard, the audio gain control on the receiver is turneddown and the program-sound level is controlled by a gain controlsupplied at the attachment.

When a program has terminated, by interrupting the direct current beingsent over the wire link long enough to enable relay 144 to becomeinoperative all subscriber receivers are reset and thereafter anothersubscription television program, for whichl a new charge may be made,can be transmitted.

Figure l0 is a circuit diagram of an arrangement for recording thepurchase of a program by means of the recording equipment 126 on thepole 124, shown in Figure 8. At each pole which distributes wire linksto a plurality of subscription television system customers, there areprovided a plurality of current relays 180. Each current relay is inseries with one of the wires of the wire link connected to the receiverattachment for the subscriber. Thus, Whenever a subscriber actuates apush-button 142, current will flow and the current relay will beactuated. Across each current Vrelay coil a condenser 182 is provided inorder to bypass thel sine wave and audio signals around the currentrelay coil.

Each current relay has a pair of contacts 180A, which when closedprovide current to make a recording. This can either be a magneticrecording or a writing stylus 184, which causes a chemical reaction bythe application `of potential to recording paper 186, which paper isgradually moved by suitable clockwork mechanism, so that the time of thepurchase may be readily detected from the location of the mark. A singleroll of paper having a plurality of tracks on paper may be employed at apole, with each track being assigned to a different subscriber, so thatthe fact of a purchase can be readily identied. Periodic removal of thepaper is rnade for accounting purposes. Alternative arrangements may beto employ magnetic tape or other media which may record the fact of apurchase by the effects of the operating potential being applied theretoand which may be read back periodically for billing purposes.

In those locations wherein service to Va community is by means ofretransmitting signals received from a re-V mote television station,either by means of coaxial cable or an antenna advantageously mountedfor receiving land rebroadcasting signals, Figure l1 shows anarrangement suitable for converting the received signals in accordancewith this invention. Expressed alternatively, Figure -11 is a circuitdiagram of an arrangement for convertingv the received standardtelevision composite video signal into a video signal having grey-levelsync pulses. It is necessary to derive horizontal blanking signals fromthe received standard `composite video signals. These 'aybe easilyderived from la televisioni `receiver-i190, located at the position ofthe retransmitter `and receiving the-broadcast vto'be retransmitted"l-The horizontal blanking -pulses Vderived 'om Vthe rei ceiver`1190areapplied to a sine wavegenerator 1911 and lto'thecontrol grid of apulse-amplifier tube 192. The output of this tube is coupled by means ofa pulse transformer `194 to a second pulse-ampliiier tube 196. Theoutput of 'this tube drives a one-shot multivibrator 198. Asis Wellknown, the one-shot multivibrator consists of two tubes 198A, 198B,which have 'their cathodes con- 'nect'ed t'o a common-cathode load 200and the control 'grid of tube 198B coupled to the anode i of tube 198Ain -a manner whereby, in the absence of-an input pulse, tube -198B-'isconducting and tube 198A is nonconducting.' When an input pulse isreceived from tube V196, tube 198B is rendered nonconducting and tube198A is rendered conducting. 'Ihis state of instability lasts for a timedetermined by the circuit components of the oneshot multivibrator. Thetime chosen for the purposes of thisv invention comprises the '-width ofthe ydesired Tgreylevel pulse, or 11 microseconds. i

iOutput from the one-'shotmultivibrat'or during the 11 microsecondinter-valet instability `is applied from the common-cathodecouplirrgfresistor 200 to'the'suppressor grid of a tube 2072, wherebythemaximum output obtainable from this tubein response tothe inputduringthis interval will be asignal having the level of a-grey-level signal.lThe control grid of the tube 202 is connected through a delay line 204to a radio-frequency input terminal 206. This terminal receives thesamelv signals as are'applied Sto the television receiver 190. Thepurpose ofthe delay line 204 is to establish theoverlap ofthe horizontalblanking pulse by lthe 'signal received from therme-shot multivibrator.As a result, the `output of the tube 262 during thehorizontalblankingpul'se"interval will be 4a Vgrey-level signal pulse;'By meansof an RF transformer 208 in the plate 'circuit of tube 202, themodified composite vide'o signal in accordance with this invention iscoupled to an ARF output terminalltl forsubsequent'retransmissioninthelmanner previously described.

Accordingly, there has been shown 'and -described herein a novel,useful, and unique arrangement for coding or rendering `aVtelevision'transmission usable *in a subscription television system.-The'transmitter-modies the television program signals vso thatano'nsubscriber or a subscriber who has not vyet purchased Vthe programwill not `be able to see an intelligible program, -nor will he be ableto receive the audio signals accompanying said program. The attachmentat'the receiver required to convert signals into a form suitable for'anintelligible display at a Vreceiver is inexpensive. VIt is'w'orth:reiterating that one of the -unique features ofthirsV invention is thatthe reconstitution of the coded video signals is performed at radiofrequency andwhile modulated' on the carrier. Thereby, any subscriberreceiver can be brought into the subscription television system bymerely connecting an attachment -betweenthe receiver antenna terminalsand the antenna. -Thef most'dicult -and troublesome portions of anyreceiver, namely, the'RF,-`IF, and synchronizing sections, need not betampered with. It is also Within the scope Vof this invention,iffdesired, to provide a coinboX at each receiver of the type describedand shown in an application for Coinbox for Subscription Television, byJohn C. Nyberg, Serial No. 706,119, led December 30, 1957, and assignedto a commonassignee. This coinbox may be provided with tone signals toenable it to operate and show a price which must bepaid before it allowsthe attachment to becomeoperative in the same manner as occurswhen thepaid-up relay becomes operative.

`I claim: l 1. A subscription television system Vcomprising a televisiontransmitter having means "for generating eeni- -po'site video signalhaving grey-level signals in place 'of `horizontal blanking andsynchronizing signals, means for generatin-g since wave signals having ahorizontal 'synchronizing signal frequency, means for transmitting `saidgenerated composite video -frequency modulated onc va radio-frequencycarrier on aiirst channel and said generated sine vwave signals on asecond channel, a receiver having means for receiving signals over saidyiirst and second channels, and means to which the outputs of said iirstand second channels are applied to generate horizontal synchronizingsignals from said grey-level signals responsive to said sine wavesignals while said greylevel signals are still modulated on saidradio-frequency carrier.

-2. A subscription television systememprising a television transmitterhaving means forV generating a composite video' signal includingsynchronizing signals, means for reducing the energy content of saidsynchronizing signals below that necessary for synchronization thereby,means for transmitting said composite video signals including saidreduced energy synchronizing signals, means at said transmitter forderiving a sine wave signal lfrom said synchronizing signal, means fortransmitting said sine wave signal over a second channel; andatelevision receiver having means for receiving signals from said irstand-second channels, and means actuated when it is desired to' view saidvideo signals and synchronized by said sine wave signals for increasingthe energy content of said synchronizing ysignals to the amount'required to aiord synchronization therewith;

3. A subscription television system comprising a television transmitterhaving Vmeans for generating a 'composite video, signal including bothhorizontal blanking signals and horizontal synchronizing signals intheblack video signal region, means for'removing said horizontal blankingand synchronizing signals from said composite video signal andsubstituting a signal having a grey -video Signal level instead, meansfor derivingsine wave signals from said horizontal blanking signals,means for transmitting said composite video signal with said grey videolevel signal over a rst transmission channel and said sine wave signalsover a second transmission channel, anda television `receiver havingmeans for receiving signals from said'irst and second channels, andmanually actuatable means forgenerating from said grey video signallevel signals responsive to said sine wave signals horizontalsynchronizing signals in said composite video signals received over saidrst channel.

4. A subscription television system comprising a television transmitterhaving means for generatingprogram audio signals, means for generatingaudio signals representative of a barker, means for generating acomposite video signal including both horizontal blanking signals andhorizontal synchronizing signals in the black video signal region, meansfor deriving sine wave signals responsive to said horizontal blankingsignals, means for removing said horizontal blanking andsynchronizingsivglnals from said composite video signal and substitutinga signal havinga grey video signal level instead, means for transmittingsaid composite video signal with said `grey video signal and said audiosignals representative of a barker over a rst channel, means fortransmitting said sine Wave signals and said program audio signals overa second channel, and a television receiver having means for receivingsignals from said'rst and second channels, manually actuatable means forinserting responsive to said sine wave signals horizontal synchronizingsignals t in said composite video signals received over said firstchannel, an audio signal reproducer in said receiver, and switch meansfor applying audio signals received from over `said rst channel when notactuated and received fromY over said second channel when actuated inresponse to actuation of said manually actuatable 11163118.

, 5, A subscription television system comprising a tele- -visiontransmitter having means'for generating program .audiosignals, means forgenerating audio signals representative lof a barker, means forgenerating a composite video signal including both horizontal blankingsignals horizontal synchronizing signals in the black video signalregion, means for deriving sine wave signals responsive' to saidhorizontal blanking signals, means for removing said horizontal blankingand synchronizing signals fromsaid composite video signal andsubstituting a signalhaving a grey video signal level instead, a sourceof potential, means for transmitting said composite video signal withsaidgrey video signal and said barker representative audio signals overa nst channel, a wireline to which said sine wave signals, said programaudio signals, and potential from said source of potential are applied,a receiver connected to said wire line, said receiver having means forreceiving signals from said lirst channel, arelay, manually operableswitch means for applying potential from said line to said relay torender it operative, means for recording the operation of said relay,means responsive to said relay being operated forinserting responsive tosaid sine wave signals received over said wire line horizontalsynchronizing signals in said composite video signals received over saidrst channel, an audio signal reproducer in said receiver to which audiosignals received from said iirst channel are applied, and meansresponsive to operation of said relay for applying audio signalsreceived from said wire line to saidfaudio signal reproducer in place ofsaid audio signals received from over said first channel.

6. A subscription television system comprising a transmitter havingmeans for generating a composite video signal having the synchronizingsignal energy content reduced below the value necessary for aiiordingsynchronization thereon, means for transmitting said composite videosignal to receivers over a iirst channel, means at said transmitter forgenerating a sine wave signal having the same frequency and phase assaid horizontal synchronizing signals, a source of potential at saidtransmitter,'means for transmitting said sine wave signals and potentialfrom said source to receivers over a second channel, and a receivercoupled to said first and second channels and having an amplifier forsaid composite video signals, means to apply exciting potential fromsaid second channel to said amplifier, manually lactuatableA means forincreasing'the gain of said amplifier responsive to said sine wavesignals to increase to the energy content value necessary for atfordingsynchronization the synchronizing signal of `said composite videosignal.L

, 7. In a television transmitter wherein there isgenerated a compositevideo signal including horizontal blanking and horizontal synchronizingsignals, means for modifying said composite video signal for use insubscription television comprising means for substituting for saidhorizontal blanking and horizontal synchronizing pulses grey-levelpulses having an amplitude less than that of said horizontal blankingpulses, means for deriving sine waves from said horizontal blankingpulses, and means for transmitting said modified composited video signaland saidrsine waves on two separate channels,

A.' 8. In a television transmitter as recited in claim 7 wherein saidmeans for modifying said composite 'video signalincludes a first and asecond rectifier bridge network-means for applying compsoite videosignals to said rst bridge network, means for applying a voltage at thelevel desired for said grey-level pulses to said second rectifier bridgenetwork, a common output terminal to which both rectifier bridgenetworks are connected, meansV for deriving wide horizontal blankingpulses which over- -signal includes a delay line, an-amplifler to;whichV said delay line is connected, means to apply said compositeVvideo signal to said delay line, a one-shot multivibrator having astable and an unstable condition, the duration of said stable conditionbeing an interval suflicient to overlap the interval of a horizontalblanking pulse, means to derive driving pulses from the horizontalblanking pulses in said delay line, means for applying said drivingpulses to said one-shot multivibrator to drive from its stablev to itsunstable condition, and means to apply output from said one-shotmultivibrator while in its unstable state'to said amplifier to reduceits gain and provide a grey-level output pulse for the duration of saidone-shotV multivibrator output.

,10. In a subscription television system of the type wherein there istinansmitted over one channelv composite video signals modulated on aradio-frequency carrier having grey-level pulses replacing horizontalblanking and horizontal synchronizing pulses and over -a second channelsine wave signals at the frequencyof and in phase with the replacedhorizontal blanking signals, a television receiver having means forreceiving signals from said rst and second channels, means actuated whendesired to view said video program for kforming pulse signals from saidsine wave signals received over said second channel, and means to whichsaid pulse signals and said iirst channel received signals are appliedfor increasing the amplitude of portions of said grey-level pulses tosubstantially restore the horizontal synchronizing pulses into saidcomposite video signals received over said first channel while saidgrey-level pulses are still'modulated on said radio-frequency carrier.`l;

1l. In a subscription television system of the type wherein there istransmitted over one channel composite video signals having grey-levelpulses replacing horif over said second channel, means for formingpulses from said sine wave signals, and means for adding said pulses tosaid composite video signals in the inputr to said amplifier. 12. In asubscription television system of the type` wherein there is transmittedover one channel composite video signals having grey-level pulsesreplacing horizontal blanking and horizontal synchronizing pulses andover` a wire link energizing potential and sine wave signals at thefrequency of and in phase with said replaced horizontal blankingsignals, an attachment for enabling a tele-V vision receiver to utilizesaid signals comprising a relay;

having a pair of normally open contacts one of which is connected tosaid wire link and the rother of which is connected to said relay coil,manually actuatable switch means to apply potential from said line tosaid relay whereby said relay is energized and latched over its owncontacts, means for recording an actuation of said switch means, apulse-forming network, means to apply sine wave signals from said relaycontacts to said pulse-forming network, an amplifier means to applyoperating potential v to said amplier from said relay contacts, means toreceive said composite video signals Aover said one channel, means toadd said composite video signals and the output of said pulse-formingnetwork, means' to connect" the output of said means to add to the inputto saidV ampliaudio signals representative of a barker, and `over a wirei link there is transmitted, energizing potential, audio signalsassociated with said video signals, and sine wave signals at thefrequency of and in phase with said replace horizontal blanking signals,a receiver for said signals having a relay having a pair of normallyopen contacts oneof which is connected to said wire link and the otherof ywhich is connected to said relay coil, manually actuatable switchmeans to apply potential from said wire to said relay whereby saidrelayv is energized and latched over its own contacts, means forrecording an actuation'V of said switch means, a pulse-forming network,means to apply sine wave signals from said relay contacts to saidpulse-forming network, `an amplifier, means for applying operatingpotential from said relay contacts to said amrpliier means to receivesaid composite video signals and barker representativelaudio signalslover said one channel and -to apply them to, said ampliiier, an audiosignal reproduced in -saidreceiven switch means for applying audiosignal output lirom said receiver, switch means for applying audiosignal output from said amplifier to said audio signal reproducer whensaid relay is not operated and for applying audio signal output yfromsaid wire link to said audio reproducer when said relay is operated, andmeans to add the output of said pulse-forming network to said compositevideo signals at the input to said ampliiier.

14, In a subscription television system of the type having a pluralityof receivers to which there are transmitted composite video signalsmodulated on a radio-frequency `carrier and reconstituting signalshaving the frequency and phase of the horizontal synchronizing signals,said composite video signals having grey-level signals in place ofhorizontal blanking and synchronizing signals, means at each receiverfor receiving said composite video signals and said reconstitutingsignals, and means to which said received signals are applied forrecreating horizontal synchronizing signals from said grey-level signals`in said composite video'signals responsive to saidreconstitutingsignalswhile said composite video signals are still modu-` lated on saidradio-frequency carrier.

15. In a subscription television system of the type having a pluralityof receivers to which there are transmitted composite video signalsmodulated on a radio-frequency carrier `and reconstitutingsignals-having the frequency and phase of the horizontal synchronizingsignals, said composite video signals having grey-level signals in placeof horizontal blanking and synchronizing signals, means at each receiverfor reconstituting said transmitted composite video signals comprisingmeans for receiving said transmitted signals, and means to which theoutputs of said means for receiving are applied for increasing the levelof a portion of each of said grey-level signals to a value suicient toaord horizontal synchronization with said composite video signals Whilesaid composite video signals are still modulated on said radio-frequencycarrier.

Y 14 s 16. In a subscription television system of the type having aplurality of receivers to which there are transmitted composite videosignals modulated on a radio-frequency carrier and vreconstitutingsignals having the frequency and phasef of the horizontal synchronizingsignals, said composite video signals having grey-level signals in placeof horizontal blanking and synchronizing signals, an attachment forconnection to the antenna terminals of a receiver comprising means forreceiving said reconstituted signals, means for receiving said compositevideo signals modulated on a radio-frequency carrier, and meansconnected to receive the signals of both said means for receiving forincreasing the level of a portion of each of the grey-level signals to avalue required for enabling horizontal synchronization of a receiver tosaid composite Video signals when demodulfated. Y

17. In `a subscription television system of the type having a pluralityof receivers to which there are transmitted 'composite video signalsmodulated on 'a radiofrequency carrier and sine wave signals h-aving thefrequency and' phase of thehorizontal synchronizing signals, saidcomposite ,video signals having grey-level signals in place ofhorizontalvblanking and synchronizing signals, an attachment forconnection to the antenna terminals of a subscriber receiver comprisingmeans for receiving said transmitted composite video signals modulatedon a radio-frequency carrier and said sine wave signals, a multiplyingmeans, and means for applying said received signals to said multiplyingmeans to enable said multiplying means responsive to said received sinewave signals to increase-the level of a portion of each of saidgrey-level sgnals to a value required to aiord horizontalsynchronization while'said composite video signals arestill modulated onsaid radio-frequency carrier.

18. In a subscription television system of the type having a pluralityof receivers to which there are trans- Vmitted composite video signalsmodulated on a radioquency and phase of the horizontal synchronizingsignals,

said composite video signals having grey-level signals in place ofhorizontal. blanking and synchronizing signals, an attachment forconnection to the antenna terminals of a subscriber receiver comprisingmeans for receiving said transmitted composite video signals modulatedon a radio-frequency carrier and said sine wave signals, means connectedto said means for receiving for adjusting the` phase of said sine Wavesignals for any deviations from the phase when transmitted, means forforming pulses from said phase-adjusted sine wave signals, a multiplyingmeans, means to apply said pulses and said received composite videosignals to said multiplying means to render it operative during saidpulse interval to increase the level of a portion of each of saidgrey-level signals to a- 2,510,046 \Ellett May 30, 1950 2,567,539 AramSept. 11, 1951 2,705,740 Druz Apr. 5, 1955

